The present invention relates to new anti-adhesion agents, i.e. products having the ability to prevent non-desired adhesion of tissues in connection with wound healing. The product has also the ability to improve healing quality by stimulating regeneration of tissue.
The invention also includes a process to prevent such undesired adhesion of tissues.
Our ability to move freely as desired and according to the current need is of utmost importance for our life quality. Suitable function of the musculoskeletal system in close cooperation with mainly the skin, mucosal membranes and nervous tissue is a prerequisite for our ability to move and requires per se that different structures such as bone, muscles and tendons are freely moveable relative to each other. Such activities require sliding zones, minimal friction and maximized freedom to move. Sliding systems between for example adjacent muscles and tendons as well as between skin and adjacent tissues are thus required for optimal function. The same is true for visceral structures, such as the gastrointestinal tract, heart, lung, brain and spinal cord. The sliding systems are formed by thin sheets of loose connective tissue, which in the abdomen, thoracic cavity, pericardial space and for the brain and spinal cord are delimited by mesothelial cells. The paratenons show a similar design.
These sliding systems are very sensitive to inflammation and injury. Scar tissues is easily formed resulting in impaired function and even loss of function. Adhesions may be formed in the abdominal cavity, i.e. formation of strings, and membrane-like fusions of adjacent or surrounding structures may eventually result in ileus, a life threatening condition. Surgical procedures carried out to treat injuries, remove tumors or treat other disorders or for performing reconstructions always result in scar formation and thereby more or less comprehensive loss of xe2x80x9cnatural and originalxe2x80x9d sliding systems.
The healing of injuries to the skin and mucosal linings are complicated, on the one hand by the restricted ability of connective tissue to regenerate and on the other hand by the formation of immature granulation tissue, which latter tissue has a limited capacity to gain a maturity similar to that of normal tissue. Thus, the dermis is neither re-formed in youths nor in adults after injury with few exceptions. Small and/or superficial injuries to the dermis are healed by replacement of the lost tissue by generation of adjacent type like structures and by the generation of reactive granulation tissue. More extensive tissue losses, such as after deep burns, third degree thermal injuries, and after loss of part of the dermis inevitably heal with scar formation, variable but persistent loss of tissue and with permanent deformations. The mechanically resistant component in the scar tissue is largely constituted by the type III collagen of short fibres and inferior organisation and has therefore inferior mechanical properties as compared to collagen of the normal optimal type I. The fraction of amorphous plastic ground substance has been reduced as well as the tissue cellularity. The number of blood vessels is with time reduced in relation to that in normal tissue and the distribution and type of vessels have changed. Wide, thin-walled vessels of inferior function as compared to the corresponding normal blood vessels are frequent, as are abnormal lymph vessel systems. The sliding systems are thus eventually replaced by rigid, fibrous collagen connective tissue.
An additionally complicating, very important factor is created by the appearance of myofibroblasts, i.e. xe2x80x9ccommonxe2x80x9d connective tissue cells (fibroblasts) which, as well as a part of the macrophages, have an increased number of cytoplasmic bundles of muscle proteins which enable the cells to slowly and powerfully contract and maintain the contraction for a long period of time. This may result in contractures which further deform and limit the function of the affected tissue. An increased presence of myofibroblasts is seen for example around breast implants (silicon prosthesis implanted for breast enlargement or breast reconstruction; a more detailed description by C. Lossing and H-A Hansson is found in an article in Plastic Reconstr. Surgery 1993, Vol. 91, page 1277-1286) and around sutures and other implants of foreign materials. Myofibroblasts are prevailing at an increased frequency around joints in certain rheumatoid diseases and may result in deviation of fingers and sometimes also in luxations. This cell is the pathogenic factor causing the deformities of the hand striking patients with Dupuytren""s contracture. The myofibroblasts as well as common fibroblasts are attached to collagen threads by means of specific heterodimeric receptors, one unit of which always is constituted by xcex21-integrin. Blocking of integrins results in elimination of contractures. Inflammation reducing drugs may influence the expression of integrins.
Sliding systems in loose connective tissue with or without a well defined sliding surface thus only restore in cases with minimal inflammation. The formation of granulation tissue occur, however, only in conjunction with an inflammatory process which per se does result in formation of immature cells and tissue components. This inability of the new tissue formed during the repair process to approach the normal differentiation levels is the reason that scar tissue is of inferior quality quantitatively and qualitatively as compared to the original, mature but lost tissue. Maturation of regenerated tissue requires access to growth factors which control and promote differentiation of cells, fibres and ground substance.
Extensive research has been directed to solve the problem of avoiding undesired adhesion of tissues in connection with the healing of wounds, for example wounds caused by surgical incisions, by accident, inflammations and tumors. PCT application No. US90/02406 describes technology associated with this specific problem and also includes a relatively extensive elucidation of the background art. The techniques described in said patent application are based on the use of sandwich constructions comprising a biodegradable bioactive membrane, the opposed surfaces of which have different composition and thereby different biological functions. However, the corresponding products do not seem to be available on the market.
Accordingly, the present invention has for an object to provide an anti-adherence agent with the use of which there is induced only a minimal inflammation of short duration, said agent being, moreover, bioacceptable and biodegradable without resulting in interfering degradation products.
Another object of the invention is to provide an anti-adherence agent having the ability to induce interface surfaces and resulting in simplified mechanical and technical handling in connection with for example surgical incisions.
Yet another object of the invention is to provide a process to prevent or substantially reduce undesirable adhesion of adjacent or surrounding tissues and organs in connection with wound healing.
A further object of the invention is to stimulate regeneration of tissue in connection with wound healing.
For these and other objects which will be elucidated by the following disclosure there is provided through the present invention a new use of chitosan and a polysaccharide immobilized thereto, said polysaccharide being selected from heparin, heparan sulfate, and dextran sulphate. While using this composition of matter there can be produced an agent having the ability to eliminate or substantially reduce undesirable adhesion of damaged tissue to adjacent or surrounding tissues in connection with wound healing.
The polysaccharide used can be immobilized to the chitosan in mainly three different ways. Thus, immobilization can take place by ionic binding, by covalent binding or by mechanical inclusion in the chitosan in connection with precipitation from solution. A process for covalent binding of the relevant polysaccharide to a substrate carrying amino groups is described in U.S. Pat. No. 4,613,665.
As a polysaccharide it is particularly preferred to use heparin or heparan sulphate said substances being commercially available on the market from several manufacturers. Also partly hydrolyzed forms of the polysaccharide can, of course, be used provided that the biological activity is maintained.
The anti-adherence agent used in accordance with the invention can be present in different physical forms, for example as films or membranes, gels, tubes or hoses, powders, aerosols or solutions. The relevant form is, of course, adapted to the damage involved. In most cases films are useful, whereas tubes or gels can be used in special cases, for example in connection with elongate confined tissues, such as muscles and tendons.
Chitosan is a linear 1,4-bound polysaccharide built up from xcex2-D-glucose amine units. The chitosan is manufactured by N-deacetylation of chitin, a polymer forming the shell of inter alia insects and shellfish. Commercially, chitin is recovered from crab and shrimp shells which constitute waste products from the fishing industry. By controlling the alkaline treatment of chitins chitosans of varying degree of N-acetylation can be made. When treating chitin with concentrated alkali, usually sodium hydroxide, N-deacetylation thus takes place, i.e. acetamido groups are converted into amino groups to form chitosan.
The physical properties of chitosan affecting its usefulness depend on the degree of N-acetylation, the molecular weight and the homogeneity. Chitosan is bio-degradable, both by chitinase in the digestive system and by lysozyme and other enzymes in the body liquids.
It is preferred in connection with the use of the present invention that the chitosan has a degree of N-acetylation of at most about 90% and preferably at most about 50%. It is particularly preferred that the degree of N-acetylation is less than about 25%.
The present invention also provides for a process to prevent or substantially reduce undesirable adhesion of tissues in connection with wound healing. This process involves applying at the site of the wound healing an agent comprising chitosan and a polysaccharide immobilized thereto selected from heparin, heparan sulphate and dextran sulphate.
Depending on the character of the wound involved the agent can be applied in the form of a film, in the form of a gel or in the form of a tube or a hose. The product to be selected for the application can easily be decided in connection with for example the relevant surgical procedure.